This invention relates to a high speed and efficient method for detecting magnetization characteristics of magnetic thin film used in magnetic recording media such as magnetic tapes, magnetic stripes of magnetic cards or magnetic discs, and to a measuring device thereof.
Along with the progress in the information society, magnetic recording media such as magnetic cards, magnetic tapes and magnetic discs have formed a considerably large market which is expected to further grow in the future. In order to stably manufacture these media in a large quantity at a low cost and improve product quality, further research and developing efforts are required. A measurement device for measuring magnetization characteristics of these media is one of the supporting means for such efforts. For example, a DC magnetization characteristic automatic recording system (Model 3257, Yokogawa Electric Corporation in Japan) and DC magnetized B-H characteristics automatic recording systems (Models BHS-40, BHH-50 and BHU-60, Riken Denshin Kabushiki Kaisha in Japan) are currently commercially available for recording the magnetization characteristics of magnetic films, such as the magnetic film on a magnetic tape.
As an example of detection by those systems, a detection method popularly used for magnetization characteristics on an annular sample will be described. When a magnetic material or an object of detection is charged with a magnetic field H, the density of the magnetic flux .PHI. generated on the material changes according to the intensity of the magnetic field H. When the magnetic field H is plotted on a horizontal axis, and the magnetic flux .PHI. on a vertical axis, a magnetization curve or a hysteresis loop is obtained. More specifically, as shown in FIG. 1, an anuular magnetic material 100 is wound with a magnetizing coil 101 (the number of windings designated N.sub.1 ) on the primary side thereof and with a detection coil 102 (the number of windings designated N.sub.2) on the secondary side thereof. The magnetization coil 101 is supplied with sine wave signal of a low frequency from a low frequency oscillator 103, and a resistance R.sub.1 is inserted in series as shown.
Since the magnetic field H in the magnetic material 100 can be regarded as proportional to the electric current I.sub.1 passing through the magnetizing coil 101, if the length of the magnetic path of the magnetic material 100 is denoted as l, the following relation holds: ##EQU1## The generated magnetic flux .PHI. is obtained by integrating the output voltage V.sub.2 of the detection coil 102. Namely, since the output voltage V.sub.c can be determined by equation (2) below. ##EQU2## The following relation therefore holds as shown below as equation (3). ##EQU3## A magnetization curve (.PHI.-H curve) can be obtained by measuring the voltages V.sub.1 and V.sub.c. If the voltage V.sub.2 is plotted on the vertical axis, the output proportional to magnetic permeability is obtained.
The magnetic material measurement system based on the above described principle is disclosed in "Yokogawa Giho" VOl. 17, No. 2, pp. 49-72, 1973. Although the measurement system is intended for universal use, as it is applicable to the measurement having a materials of high permeability such as plates or blocks of permanent magnets, magnetic powder, magnetic thin film, etc., the measurement system is still not entirely free of problems in performance, operability and price. Moreover, when used for measuring magnetic stripes prepared by thermal transfer or application on a paper card, a card or a passbook on which magnetic tapes are pasted, or a magnetic card coated on its surface in magnetization characteristics, a sample 110 of the magnetic thin films should be cut out from the card or book as shown in FIG. 2, adjusted in size to accommodate the size of the system, and sorted in a layer of about ten cards before being subjected to the actual measurement. The system therefore is extremely cumbersome. The measurement system, moreover, is incapable of measuring the magnetization characteristics of magnetic stripes on a magnetic card as incorporated on the card. It was heretofore extremely difficult to measure the absolute value of the magnetization characteristics of a magnetic stripe medium, a magnetic disc medium or the like.
A relation evaluation method for a standard medium is established as a compatibility standard by, for instance, JIS (Japanese Industrial Standard) No. B 9560-1979 and JIS No. 6291-1986. However, since these evaluation methods include the effect of the magnetic field from the magnetic head, the characteristic value of a particular medium per se cannot be clearly determined. The prior art method is further detrimental in that a user should visually read saturation magnetic flux, residual magnetism, holding force, and other magnetization characteristics from the hysteresis curve which is drawn on a sheet of paper with an X-Y recorder and calculate them in order to determine the quality of the magnetization characteristics, which is quite energy- and time-consuming. There is not yet developed no a system which can measure the distribution of the magnetization characteristics of a magnetic striped medium or that which can analyze the process capability of those magnetization characteristic values. If the above mentioned measurement system is used to measure plural points on the magnetic thin film of a magnetic head (single head type), a moving mechanism for the magnetic head or the medium becomes necessary.
There has been proposed a method for measuring by means of plural magnetic heads (multi-head type). For instance, the data on the first location on a magnetic thin film is read in the first period without switching the channel of the output voltage of a multi-head, and the data on the second location on the magnetic thin film is read in the next period. However, this method is detrimental in that it requires a long period of time for the measurement unless a high frequency wave is used as an excitation signal. However, if high frequency wave signal is used, an eddy current is generated on the medium per se at the time of measurement and affects the result. The system currently available in the market are extremely large sized because individual components such as an excitation device, an integrater for signal processing, a recorder, etc. are merely combined.